The temperature and efficiency of a gas turbine have become high in recent years, and according to this a turbine blade also tends to increase in height (become longer and larger). In particular, since thermal energy of a combustion gas to be exhausted needs to be suppressed in a turbine blade of the rear stage, the height of the blade is significantly increased. Since the number of vibrations is reduced with the increase of the height of a blade in such a turbine blade, the possibility that an unstable vibration mode such as flutter occurs is increased.
Therefore, a tip shroud is disposed at the tip of a blade body of each turbine blade to increase structural damping, so that the occurrence of the unstable vibration mode is suppressed. Since the tip shroud also needs to be cooled as the temperature of the gas turbine becomes high, a cooling system is formed in the tip shroud.
An example of such a cooling system is disclosed in Patent Document 1, where a cavity communicating with cooling passages in the blade body is formed in the tip shroud so that cooling air having cooled the blade body can be used to cool the tip shroud. This cavity is formed by forming a recess which communicates with the cooling passages in the tip shroud and closing an opening of the recess with a plug. Accordingly, cooling air is introduced into the cavity and a cooling medium is supplied to the outer periphery of the tip shroud via the cavity, so that the tip shroud is cooled.
Furthermore, Patent Document 2 discloses a technique where a mounting groove is formed on each of a pair of side surfaces of the recess and the cavity is formed by closing an opening of the recess by insertion of the plug into the mounting grooves in order to prevent the plug from coming off due to a centrifugal force generated by the rotation of a rotor. More specifically, the mounting grooves of Patent Document 2 are formed so as to face each other in the axial direction of the rotor, and the opening is closed when one plug is inserted into the mounting grooves in the circumferential direction.